Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon

Juan J Torres-Vega,Alicia Torre,Diego R Alcoba,Ofelia B Oña,Rodrigo Báez-Grez,Víctor García,Alejandro Vásquez-Espinal,William Tiznado,Luis Lain

doi:10.3390/chemistry3040080

Abstract

The minimum energy structures of the Si3C5 and Si4C8 clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment.

Highlights

For the sake of clarity, our analysis will be divided into two parts: the chemical bonding analysis according to the electronic localization function (ELF)-LOC method and the global and local aromaticity analysis according to magnetic criteria
Chemical Bonding Analysis According to the ELF-LOC Method
The orbital localization provided by the ELF-LOC method reveals a chemical bonding pattern similar to that described by adaptive natural density partitioning (AdNDP), as shown in Figures 1 and 2

Summary

Introduction

The concept of aromaticity has been extended over time to coin new features that define a system as aromatic and address a diversity of organic and inorganic systems [1,2,3,4,5]. In this regard, nowadays the concept of aromaticity, π and σ, is used extensively to rationalize the stability of some atomic clusters [6]. Along with π- and σ-aromaticity, multiple local π-aromaticity shows to be a helpful concept for rationalizing complex conjugate systems, such as polycyclic hydrocarbons or graphene [20,21]. It was indicated that the concept of multiple local σ-aromaticity is applicable in the chemistry of nonagermanide clusters [22]

Methods

Results

Conclusion